For safely using duplex stainless steel and super duplex stainless steel, temperature-pH domains of stress corrosion cracking (SCC) resistance were provided by using slow strain rate testing (SSRT) screening in sour conditions in an earlier study.

To follow-up the study, a failure analysis has been performed on the tube material of UNS S32750 and the specimens after the SSRT in a sour environment in pH 2.8, pH 3.5 at 80 °C. Scanning electron microscope (SEM) equipped by energy-dispersive X-ray spectrometer (EDS) analysis and Electron backscatter diffraction (EBSD) measurements have been used for the investigation on specimen surface, fracture surface and cross-sections of the SSRT specimens. Initiation of selective dissolution (SD) and cracking has been identified. EBSD reveals that cracking initiated in ferrite with enhanced strain/deformation in frontend of selectively dissolved austenite, where possible SCC mechanism seems to be hydrogen embrittlement. It observed that SD stopped in the brittle-ductile transition area in the fracture surface, which probably attributed to repassivation of the material in the condition of pH 3.5. Combined SSRT and analysis methods by SEM and EBSD showed a good way for the material evaluation before decision making for the materials selections and supplementary long-term exposures.

Subject
Scanning electron microscopy, Materials, Secondary cracks, Tubes, Sour environments, Crack initiation, Fracture surfaces, Crack propagation, Acidity, Selective dissolution, Ferrite, Stress corrosion cracking, Austenite
Keywords:
Duplex stainless steel (DSS), super duplex stainless steel (SDSS), stress corrosion cracking (SCC), selective dissolution (SD), scanning electron microscope (SEM) equipped by energy-dispersive X-ray (EDS) analysis, and electron backscatter diffraction (EBSD) measurement
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2022
Association for Materials Protection and Performance (AMPP)
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